Interesting, not sure if this is news
If the best example of writting by BioWare is Baldur's Gate 2 or Dragon Age: Origins, and the best example of Black Isle (Avellone) is Planescape: Torment, then the later completely mogs the floor with the former.
Not only because Torment has much greater atmosphere, characters and plot - which it has; but because there's something inherently vulgar and repelling about all BioWare games. Both in the more wide sense of the world and the original sense of lowly mundane. There's something about their writing and aesthetics that never stop crossing as ungenuine and mockery, even if not always present. Meanwhile Torment, which is set on a weirder and stranger world never rubbed me that way. Everywhere you go the characters are fun, serious, crazy, adorable or despicable, but never ungenuine. The stories told, including those that are not the main one are cautivating and the ending is truly moving. On top of being set on an exotic setting which is invariable harder to set in motion.
Any hack can take a world and fill it with idiocy, jokes and general unseriouness. Mid or decent writers can take generic and safe worlds like Forgotten Realms and make stories equally mid on it. But it takes more than a pinch of real talent to make a genuine story in a strange place like Planescape. These Bioware guys were never as good as they think they were.